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Author Topic: Advice on a balancing radiators with GSHP  (Read 3599 times)
andrewellis
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« on: September 25, 2018, 09:43:37 AM »

I am after some advice on this tricky problem.  I haven't fitted all my radiators yet so am waiting on them all going in before balancing. However everything I have read on balancing is predicated around a normal CH system at 70 C or so.  They then talk about achieving 10 degrees across the radiator.  However the GSHP modulates to achieve varying difference between the input and the return.  This is often much less than 10C.  My house is very long with some large radiators at the start of the run and the end radiators I think could do with a bit more flow at the far end radiators.  I have bought a cheap two wire thermometer and was wondering what people recommend as a process for balancing GSHPs.
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linesrg
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« Reply #1 on: September 25, 2018, 10:59:14 AM »

Andrew,

I know there is a thread here on the forum about how to balance radiators in a normal heating system but I have run CH systems in three different houses and found that the thermostatic valves have been more than adequate.

OK so starting from cold it takes some time for the system to become 'balanced' but, personally I've never been convinced of the need to 'faff about' with a more precise set-up.

As I have reported elsewhere my biggest challenge was when the dedicated Danfoss pump for the two UFH rooms 'cut in' effectively stealing a large part of the circulating water. Now the Honeywell automatic bypass has been installed and the pump taken away the system 'manages itself'.

Just a personal view.

Regards

Richard 
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andrewellis
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« Reply #2 on: September 25, 2018, 12:43:24 PM »

Hi Richard,
Ah interesting, I am missing a radiator in the first room as the thing arrived bent from the manufacturer :<. That does make a lot of sense.  I had left all the TRVs fully open but I shall have a fiddle.  I can see my poor wife putting up with me wandering round with my arduino thermometer fine tuning the heck out of the system for the next few weeks.
Thanks
Andrew
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RIT
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« Reply #3 on: September 25, 2018, 04:33:22 PM »

Don't forget that a lot about balancing is about providing a level of resistance to the water flow so that it does not just find the shortest path. The idea is to 'balance' the water flow across all the possible paths in the home.

If you just depend on the TRVs you can end up with most of the flow going via one loop. The TRVs then kick in once the room has reached the correct temperature and then the flow gets diverted to the next preferred path. This is a very slow way to heat up a home if you wish to send heat to many locations at once. Also, the process could be slowed even more as the boiler may turn itself off for a while as the return temp will rise very quickly - so the boiler can be off at the time the TRVs start to operate. No additional heat will be added to the system until the boiler cycles its pump and receives cooler water from other parts of the system.

You can use this as a way to do the balancing. On a cold day start the heating and just find the rads that have become hot after 2-3 mins. If these are not the ones you want to work first, just tighten their value(s) a little. Repeat over time and your system should be good enough. Having working TRVs means the system does not have to be perfectly balanced.
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eabadger
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« Reply #4 on: September 25, 2018, 05:41:05 PM »

as above.
as a rule of thumb ones further away need opening more or fully, or as above all the heat will go to nearest and the boiler will shut off, so nearest ones almost closed on the gate valve

steve
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knighty
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« Reply #5 on: September 25, 2018, 06:22:12 PM »

the taps on the ends of the radiators... not the one you use to turn the temperature up/down on/off, the other side

turn them all the way off then back on 1/8 of a turn.... do that on every radiator when they're cold

then turn the heating on... give them 20min to warm up, see which radiators get hot and which ones don't...  any that don't get hot turn them up another 1/8 or a turn, give it another 20min and check again
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desperate
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« Reply #6 on: September 25, 2018, 06:56:01 PM »

Absolutely what Knighty said, just remember while balancing turn all the TRVs fully open, then when you are done adjust them as you wish.

Desp
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andrewellis
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« Reply #7 on: September 25, 2018, 07:30:08 PM »

Thanks for your advice.  I shall give it in a few days when this heat wave passes.
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Philip R
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« Reply #8 on: September 25, 2018, 08:56:17 PM »

Radiators near the circulating pump need pulling in on the lockshields. Most of the valve orifice restriction action happens in the first 1.5 turns open from fully closed.

Only numptys open all the the lockshields to max and then set the circ pump to maximum speed.

I cannot believe that today in the age of the condensing boiler, we in the UK still design heating systems to operate at 70 deg C.
Do yourself a favour and plumb your rads the way it is done in Germany and Holland ( And my hose too) which is top end in bottom end opposite out.

Guarantetes a better stratification and cooler water exiting the rad back to the boiler / heat source.

Philip R
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desperate
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« Reply #9 on: September 25, 2018, 09:03:13 PM »

TBOE in 11/2" gas barrel and make it look like an old gravity system Grin if you have a 24" stillson to do it all up with

Desp
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Philip R
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« Reply #10 on: September 25, 2018, 09:19:42 PM »

My late grandparents home in Munich was plumbed in steel threaded pipe in 1956. The cellar plumbing was like a that in a small ship.
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pantsmachine
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« Reply #11 on: September 25, 2018, 11:09:31 PM »

I have long runs in the house and found that at the end of the process the rad closest to the boilers lockshield was only a squeak from closed while the rad furthest was almost fully open.

I look for a 12 degree drop across the radiator.
Fire up system with all TRV's wide open
Let system get up to temp
Start at the rad closest to boiler
Slowly close or open the lockshield valve until you see a 12 degree drop across rad from incoming temperature to outgoing temperature.
Work through the rest of the house rads in order next closest and finish at furthest away.

That's it. Set your TRV's to your room specific req's and accept that through expansion and contraction your Lockshields will move a little so there may be a minor adjustment or two but that's the system balanced and working efficiently.
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andrewellis
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« Reply #12 on: September 26, 2018, 09:04:33 AM »


Do yourself a favour and plumb your rads the way it is done in Germany and Holland ( And my hose too) which is top end in bottom end opposite out.

I wondered about this when reading the radiator manual and yet I never see this set up in the UK. Significantly better energy extraction by their stats.


I look for a 12 degree drop across the radiator.

I think it was your mention of balancing elsewhere that made me have another look at the process.  I was wondering if 12 degrees is still valid for a GSHP.  Google isn't bringing anything up with regards to balancing heat pump systems. It seems to modulate the heating medium pump down to achieve little more than a 5C split.  I was thinking of artificially bringing the temperature up by calling for a 30 degree room temperature and balancing whilst the water then hot.
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knighty
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« Reply #13 on: September 27, 2018, 06:56:53 PM »

as long as your radiators are balanced so they're all about the same temperature, the temperature drop across them doesn't really matter

there's no point restricting system flow down to increase the temperature drop across the radiators

12'C is much too large of a temp drop for a GSHP when you have much lower flow temperatures... radiator temp should be about average between the flow and return temps, so if you have in at 40'C and out at 28'C (12'C lower) you're average temp is only 34'C... which is pretty low :-o

do you have a thermal store or is the heating circuit heater directly by the heat pump?


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andrewellis
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« Reply #14 on: September 27, 2018, 10:35:19 PM »

do you have a thermal store or is the heating circuit heater directly by the heat pump?

It is directly heating the loop.  The Nibe regulates down so there has been no need for a thermal store/buffer.  At the moment the flow is 34.3C and return 28.3C with the heat medium pump running at 27%.  Between 5 and 6 degrees split seems to be what I have seen most of the time at those temperatures.  When we hit 40C flow the other day there was a 7 degree split. 
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